An Iron Furnace at Work
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The Work Force Raw Materials of Iron Making 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 oxide is heated in an intense flame fed by a carbon fuel. Oxygen in the ore combines with carbon monoxide released from the fuel and is expelled as CO 2 . 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 “flux,” usually limestone, is added. The flux combines with the impurities in the ore and forms slag. The basic ingredients of iron making—iron ore, limestone, and carbon fuel—are some of the most common materials on Earth, but are not found every- where. Early furnaces were built where these materials were avail- able. Iron is usually found in combination in the form of hem- Historians have styled rural iron making opera- tions like Hopewell’s, called “iron plantations,” as feudal. This was a self-sufficient community of craftsmen and laborers living lives directly or indirectly governed by the furnace. It could be a difficult taskmaster—dirty, noisy, dangerous at times, ever needing to be fed and tapped. But a demanding furnace also meant community pros- perity. A silent furnace meant lean times. A traditional hierarchy governed the furnace’s operations. At the pinnacle was the ironmaster, director of the enterprise and often an owner. Good ironmasters had to be financier, techni- cian, bill collector, market analyst, personnel director, purchasing agent, and host to prospec- tive buyers. His was a volatile job: bad luck or poor judgment usually meant failure. Success often brought wealth. A clerk helper kept the books, ordered supplies, served as paymaster, and managed the office store. The job well per- formed could be a stepping stone to ironmaster. The quality of the iron was in the founder’s hands. His job: keep the furnace blowing at peak efficiency. He supervised the other furnace workers: keepers helped him monitor the fur- nace and took the night shift; fillers charged the furnace with raw materials; and guttermen di- rected molten iron as it flowed from the fur- nace. Moulders, the highest-paid workers, had Chimney: Smelting by- products—CO and CO2 gases and smoke—are expelled. Tunnel Head: Limestone, iron ore, and charcoal are dumped into the furnace. Air Duct: Air under pres- sure is brought from air blast machinery. Tuyere: Narrowing pipe directs air blast into the crucible, where tempera- ture is boosted to 2,600°–3,000°F. Bosh: Iron is becoming molten; with slag, it de- scends towards crucible. Crucible: Narrowest and hottest part of furnace, where iron becomes fully molten. Hearth Stone: Molten iron and slag settle on this stone. Dam Stone: Holds mol- ten iron and slag in hearth until the slag is drawn off and the iron is tapped. To make the most money from molten iron you would cast finished products at the furnace. Moulders cast several items: plowshares, pots, sash and scale weights, cannon, and shot. But as iron stoves grew more common in 1800s homes, Hope- well built its opera- tion on stove plates. Cast products made profits, but the age also demanded goods that the furnace’s brit- tle high-carbon iron was not suitable for. The tough, malleable wrought iron needed for plow moldboards, PHOTOGRAPHS NPS / GEORGE FISTROVITCH ILLUSTRATIONS NPS / L. KENNETH TOWNSEND atite, the magnetite used at Hopewell, or other iron ores. Most iron ore was dug in small surface mines. Any substance that contained calcium, like sea shells, could be used as a flux, but for most furnaces, lime- stone was cheap and abundant. American forests were so vast—and bringing in coal so expensive before railroads were built—that early iron plantations like Hope- well made their own fuel. They slowly burned carefully built piles of wood to make charcoal, an almost purely carbon fuel that burns with in- tense heat. The great demand for charcoal meant that early fur- naces were sited on woodlands. One other ingredient was need- ed: air. It was directed into the hearth under pressure by the water- powered blast ma- chinery, raising the fire in the furnace to smelting temperature. They tended the furnace, the glowing heart of their community; it yielded iron and a way of life. The Moulder’s Art Finished Products Furnace Operations Iron plantation life revolved around the always- running, roaring furnace. It shut down usually once a year—to refurbish its inner walls and hearth. While it was “in blast,” its cycles of filling and tapping set life’s rhythm at Hopewell. It de- manded close attention. Workers constantly fed it, watched its flame, and listened to the sound of its blast. For workers around the furnace, it was a hot, hard job requiring protective shoes and aprons. Every half-hour fillers dumped into the tunnel head 400 to 500 pounds of iron ore, 30 to 40 pounds of limestone, and 15 bushels of charcoal. With no gauge, the founder used his practiced eye to judge the shape and color of the flame from the chimney and the color and consistency of the molten iron. This told whether the temperature was right and the proportions The founder was boss, technician, and trouble- shooter. He directed the ceaseless round of activity at Hopewell Furnace. Raw materials —iron ore, limestone, and charcoal—were supplied by miners, woodcutters, and col- liers and transported by teamsters. Fillers carted materials from the charcoal house area to the bridge house and dumped them at the tunnel head. Gut- termen and moulders stood ready below to skim off the slag and cast the molten iron when it was tapped by the founder. In the “flask casting” method of casting, both sides of a stove plate were molded. This let the moulder produce a relatively light, curved plate. The flask was two wooden frames. The moulder laid the bot- tom half, the “drag,” on a piece of wood called the “follow board,” placing the wooden pattern in- side. He then sifted fine sand over the pattern and packed the rest of the drag with coarse, damp sand 1. After scraping away excess sand with the “strike” 2, he placed another follow board on top and turned over the drag. He then removed the first follow board, blew away loose sand from the edges of the pattern with a bel- lows 3, and “dressed” the edge with a moulder’s spoon. He attached the “cope,” the flask’s top half, to the drag and again added fine and coarse sands. Before packing the sand he inserted a wooden wedge to form a “gate” 4, al- lowing the molten iron to enter. Next he removed the wedge, separated drag and cope, and carefully removed the pattern with a pair of lifters 5. He next secured the two halves of the flask with iron clamps. The final step was to pour the molten iron 6 through the gate. After the iron had cooled, he separated the halves of the flask and removed the gate from the plate. Other workers brushed off sand and filed rough edges, readying the plate for market. Cast House Air Blast Machinery Founder Iron Ore Limestone Charcoal Collier Cooling Shed Air Duct Founder Charcoal House Connecting Shed Bridge House Tunnel Head 1 5 4 3 2 1 2 4 5 6 3 7 8 1 2 4 5 6 3 7 Moulder Molten Iron and Slag Descend of ingredients correct. In temperatures that could reach 3,000°F, the molten iron flowed down toward the hearth, to be tapped when the founder judged it ready. At Hopewell he generally tapped the furnace every 12 hours, at 6 am and 6 pm. After the guttermen drew off the slag, the iron could be tapped in two ways: It could flow directly into the “pig bed” in the cast house floor (it looked like a litter of nursing pigs), where it hardened into pig iron ready for market. Or it could be tapped into large ladles, then cast in molds (see Moulder, bottom center). This process was repeated twice daily as long as the furnace was in blast. the exacting job of casting the iron. Colliers (charcoal makers), miners, and woodcutters provided the raw materials for the furnace. Other workers included teamsters, who drove the wagons carrying raw materials and finished products; cleaners, often women and children, who finished the cast products; and teachers. Women supplemented family incomes by sew- ing, lodging and boarding single workers, and laundering. Some made extra income working as woodcutters and miners. Farmers fed the community, and some worked the furnace for part of the year. African Americans also worked furnaces—enslaved at first, later as temporarily employed runaway slaves and free blacks. 6 8 Slag Iron Gutterman An Iron Furnace at Work nails, and horseshoes had to be obtained through an indirect process not in place at Hopewell. The molten iron was cast into pig iron bars shipped else- where for refining. Receiving Box Blowing Tubs was oxidized, raising the melting point. The iron partially solidified into a pasty lump. The lump was then beaten to drive out the slag and align the fibers, producing wrought iron. More processing converted this iron into the bars and rods used by blacksmiths. A lengthier process was used to convert iron to steel. Hope- well’s owners often held interests in local forges and mills. At a finery forge, the iron was remelted and much of its carbon HOFU_LayoutFinal_S2.indd 1 4/19/11 10:04 AM
Transcript of An Iron Furnace at Work
The Work Force
Raw Materials of Iron Making
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 ore and forms slag.
The basic ingredients of iron making—iron ore, limestone, and carbon fuel—are some of the most common materials on Earth, but are not found every-where. Early furnaces were built where these materials were avail-able. Iron is usually found in combination in the form of hem-
Historians have styled rural iron making opera-tions like Hopewell’s, called “iron plantations,” as feudal. This was a self-suffi cient community of craftsmen and laborers living lives directly or indirectly governed by the furnace. It could be a diffi cult task master—dirty, noisy, dangerous at times, ever needing to be fed and tapped. But a demanding furnace also meant community pros-perity. A silent furnace meant lean times.
A traditional hierarchy governed the furnace’s operations. At the pinnacle was the ironmaster, director of the enterprise and often an owner. Good ironmasters had to be fi nancier, techni-cian, bill collector, market analyst, personnel director, purchasing agent, and host to prospec-tive buyers. His was a volatile job: bad luck or poor judgment usually meant failure. Success often brought wealth. A clerk helper kept the books, or dered supplies, served as paymaster, and managed the of fi ce store. The job well per-formed could be a stepping stone to ironmaster.
The quality of the iron was in the founder’s hands. His job: keep the furnace blowing at peak effi ciency. He supervised the other furnace workers: keepers helped him mon itor the fur-nace and took the night shift; fi llers charged the furnace with raw materials; and guttermen di-rected molten iron as it fl owed from the fur-nace. Moulders, the highest-paid workers, had
Chimney: Smelting by-prod ucts—CO and CO2 gases and smoke—areexpelled.
Tunnel Head: Limestone, iron ore, and charcoal are dumped into the furnace.
Air Duct: Air under pres-sure is brought from air blast machinery.
Tuyere: Narrowing pipe directs air blast into the crucible, where tempera-ture is boosted to 2,600°–3,000°F.
Bosh: Iron is becoming molten; with slag, it de-scends towards crucible.
Crucible: Narrowest and hottest part of furnace, where iron becomes fully molten.
Hearth Stone: Molten iron and slag settle on this stone.
Dam Stone: Holds mol-ten iron and slag in hearth until the slag is drawn off and the iron is tapped.
To make the most money from molten iron you would cast fi nished prod ucts at the furnace. Moulders cast several items: plowshares, pots, sash and scale weights, cannon, and shot. But as iron stoves grew more common in 1800s homes, Hope-well built its opera-tion on stove plates.
Cast products made profi t s, but the age also de manded goods that the furnace’s brit -tle high-carbon iron was not suita ble for. The tough, mal leable wrought iron needed for plow moldboards,
PHOTOGRAPHS NPS / GEORGE FISTROVITCH
ILLUSTRATIONS NPS / L. KENNETH TOWNSEND
atite, the mag netite used at Hopewell, or other iron ores. Most iron ore was dug in small surface mines. Any substance that contained calcium, like sea shells, could be used as a fl ux, but for most furnaces, lime-stone was cheap and abundant.
American forests were so vast—and bringing in coal so expensive before railroads were built—that early iron plantations like Hop e-well made their own fuel. They slowly burned carefully built piles of wood to make char coal, an almost purely carbon fuel that burns with in-
tense heat. The great demand for charcoal meant that early fur-naces were sited on woodlands. One other ingredient was need -ed: air. It was dir ected into the hearth un der pressure by the water-powered blast ma-chinery, raising the fi re in the furnace to smelting temperature.
They tended the furnace, the glowing heart of their community; it yielded iron and a way of life.
The Moulder’s Art Finished Products
Furnace Operations
Iron plantation life revolved around the always-running, roaring furnace. It shut down usually once a year—to refurbish its inner walls and hearth. While it was “in blast,” its cy cles of fi lling and tapping set life’s rhythm at Hopewell. It de-manded close attention. Workers constantly fed it, watched its fl ame, and listened to the sound of its blast. For workers around the furnace, it was a hot, hard job requiring protective shoes and aprons. Every half-hour fi llers dumped into the tunnel head 400 to 500 pounds of iron ore, 30 to 40 pounds of limestone, and 15 bushels of charcoal. With no gauge, the founder used his practiced eye to judge the shape and color of the fl ame from the chimney and the color and consistency of the molten iron. This told whether the temperature was right and the proportions
The founder was boss, technician, and trouble-shooter. He directed the ceaseless round of act iv ity at Hopewell Furnace. Raw materials —iron ore, limestone, and charcoal—were supplied by miners, woodcutters, and col-liers and transported by teamsters. Fillers carted materials from
the charcoal house area to the bridge house and dumped them at the tunnel head. Gut-termen and moulders stood ready below to skim off the slag and cast the molt en iron when it was tapped by the founder.
In the “fl ask casting” meth od of casting, both sides of a stove plate were molded. This let the moulder pro duce a relatively light, curved plate. The fl ask was two wooden frames. The moulder laid the bot-tom half, the “drag,” on a piece of wood called the “follow
board,” placing the wooden pattern in-side. He then sifted fi ne sand over the pattern and packed the rest of the drag with coarse, damp sand 1. After scraping away excess sand with the “strike” 2, he placed another follow board on top and turned over the drag.
He then removed the fi rst follow board, blew away loose sand from the edges of the pat tern with a bel-lows 3, and “dressed” the edge with a moulder’s spoon. He at tached the “cope,” the fl ask’s top half, to the drag and again added fi ne and coarse sands. Before packing
the sand he in serted a wooden wedge to form a “gate” 4, al-lowing the molten iron to enter. Next he removed the wedge, separated drag and cope, and carefully removed the pattern with a pair of lifters 5. He next secured the two halves of the fl ask with iron clamps.
The fi nal step was to pour the molten iron 6 through the gate. After the iron had cooled, he separated the halves of the fl ask and removed the gate from the plate. Oth er workers brushed off sand and fi led rough edg es, readying the plate for market.
Cast House
Air Blast Machinery
Founder
Iron Ore Limestone Charcoal
Collier
Cooling Shed
Air Duct
Founder
Charcoal House
Connecting ShedBridge House
Tunnel Head
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Moulder
Molten Ironand Slag Descend
of ingredients correct. In temperatures that could reach 3,000°F, the molten iron fl owed down toward the hearth, to be tapped when the founder judged it ready. At Hopewell he generally tapped the furnace every 12 hours, at 6 am and 6 pm. After the guttermen drew off the slag, the iron could be tapped in two ways: It could fl ow directly into the “pig bed” in the cast house fl oor (it looked like a litter of nursing pigs), where it hardened into pig iron ready for market. Or it could be tapped into large la d les, then cast in molds (see Moulder, bot tom center). This process was repeated twice daily as long as the furnace was in blast.
the exacting job of casting the iron. Colliers (charcoal makers), miners, and woodcutters provided the raw materials for the furnace. Other workers included team sters, who drove the wagons carrying raw materials and fi nished products; cleaners, often women and children, who fi nished the cast products; and teachers. Women supplemented family incomes by sew-ing, lodging and boarding single workers, and laundering. Some made extra income working as woodcutters and miners. Farmers fed the community, and some worked the furnace for part of the year. African Americans also worked furnaces—enslaved at fi rst, later as temporarily employed runaway slaves and free blacks.
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8SlagIron
Gutterman
An Iron Furnace at Work
nails, and horseshoes had to be ob tained through an indi rect pro cess not in place at
Hope well. The molten iron was cast into pig iron bars shipped else-where for refi ning.
Receiving Box
Blowing Tubs
was oxidized, raising the melting point. The iron partially solidifi ed into a pasty lump. The lump was then beaten to drive out the slag and align the fi bers, produ c ing wrought iron. More processing converted this iron into the bars and rods used by blacksmiths.
A lengthier pro cess was used to convert iron to steel. Hope -well’s owners often held interests in local forges and mills.
At a fi nery forge, the iron was remelted and much of its carbon
HOFU_LayoutFinal_S2.indd 1 4/19/11 10:04 AM
