Iron production

From Iron Allentown Wiki
Revision as of 12:07, 26 September 2018 by Dmgrieder (talk | contribs)
Jump to navigation Jump to search

Iron production converts iron ore into pig iron through a process known as smelting at a furnace. Early in the history of iron production in the US, most furnaces used charcoal as fuel, so charcoal production and iron production were often closely linked. Ironworks are some of the first and most enduring examples of industry in the United States, and remnants of them survive particularly well in rural parts of the country. [1]

History

In the eighteenth and nineteenth centuries, small-scale metalworking operations produced everyday objects like many forms of kitchenware, toys, building materials, and tools. [2] Iron plantations were rural communities that often included forges, housing for workers, woodlands for charcoal production, and a sawmill [3]. Bloomeries were were early centers of liited iron production. In a bloomery, the iron oxides in ore were reduced to metal and metal was separated from gangue in the ore. The fire created liquid slag and burning charcoal produced carbon dioxide reduced the oxide to metallic iron. Blast furnaces were also used for larger-scale iron production. These furnaces could be 25 to 30 feet high and had hollow centers into which was placed ore, fuel, and flux. Bellows were powered by a water wheel and melted iron and liquid slag accumulated in the bottom of the furnace. [4] By the nineteenth century, blast furnaces were the most common. [5]

Iron Communities

Self-sufficient communities, called iron plantations, were built around these furnaces. Many workers were needed to run an iron plantation, including colliers, miners, woodcutters, molders, founders, patternmakers and their helpers. Hopewell Furnace, in Pennsylvania, employed roughly 200-250 people in the nineteenth century. Workers at iron plantations would often bring their families along with them, so the community at Hopewell Furnace would have consisted of about 600 people. [6] The lands of iron plantations would include housing, gristmills and sawmills, farming land, and vast amounts of woodland, as well as barns, company stores, springhouses, blacksmiths, schools, churches, carpenter's shops, forges, casting houses, charcoal storage, and many other buildings. [7]

Fuel

Prior to the 1830s, every furnace in the US burned charcoal as fuel. Charcoal was used because it could be produced in large quantities, it burns hotter than wood, and it is almost pure carbon, so it reduces impurities in iron produced. [8] To make charcoal, a variety of methods were used including hearths and kilns. Hearths were generally used in the pre-Civil War period and involved burning wood in earth-covered mounds. Kilns were made of brick and were more efficient. They also created more durable charcoal than hearths, which yielded more brittle charcoal. [9] Around the 1860s, coal and coke began to replace charcoal in some areas, but overall iron production increased so much that the use of charcoal still continued to rise up to 1890, and the last charcoal-powered furnace in the US was in blast until 1945. [10]

Operation

Efficiency was known to be inconsistent between furnaces in different places and at different times. Factors affecting this include differences in furnace construction and operation, as well as varying compositions of iron ore and qualities of charcoal used. [11] Ironworks had to be near water and sources of raw materials such as charcoal, limestone, and iron ore. [12] Colonial ironworks used a variety of techniques to produce iron.

Bloomery

A bloomery was a small operation that heated iron ore to refine and shape it, producing wrought iron. Bloomeries needed simple equipment like a hearth, a bellows, and a tool for manipulating the iron. Bloomeries were common in colonial America, and operated between the seventeenth and twentieth centuries. Disadvantages of bloomeries include limited production, wasted heat, and an inability to completely separate the iron from slag.[13]

Blast Furnace

Blast furnaces addressed many of the disadvantages of bloomeries. They could be run continuously for months at at time and conserved heat, and they could produce much more iron. Blast furnaces were vertical, hollow structures, the top of which would be loaded with ore, fuel, and flux, while the bottom had air vents and a hole for the molten iron to run out. Blast furnaces tended to be 25-30 feet high at first, and eventually grew to 32-40 feet high in the nineteenth century. They had very thick stone walls, with fire-resistant interior lining. A layer between the lining and outer stones, usually made of clay or smaller stones, provided better insulation and allowed the inner walls to expand slightly when heated. Bellows, which pumped air into the furnace to feed the flames, were often powered by waterwheels, equal to about 20 horsepower. By adjusting ventilation, the temperature inside blast furnaces could be controlled to a degree. Because blast furnaces were loaded from the top, they were often located along hillsides. When the molten iron was ready to be collected, or tapped, smaller hole at the top was opened to allow the liquid slag, which sat on top of the iron because it was lighter, to be drawn away. After the slag was collected, the main plug was pulled, and the molten iron ran into sand molds. The iron produced in blast furnaces is called pig iron because the final product resembles piglets suckling on their mother. After the iron ran into the molds and was cooled, the "pigs" were broken off the "sows." These smaller pieces were more valuable than the metal in the runners which would need to be remelted. [14]

Finery

Finery converted pig iron to wrought iron, and was introduced to North America in the seventeenth century. Some types of finery required the use of charcoal because coal introduced too many impurities to the iron. There were at least four types of finery used in the United States.

Walloon Process

The Walloon Process was the original fining technique. The Walloon Process involved pushing a pig of iron into a hearth full of charcoal at a downward angle to melt it, working it into a mass called a loup, and hammering it to expel slag. The Walloon Process required a lot of air to heat the flames and the quality of wrought iron produced was heavily dependent on the skill of the workers making it. [15]

Lancashire (Charcoal Hearth) Process

Lancashire Process involved moving the pig iron through the hottest part of a flame to burn off impurities and allowing the melted iron to accumulate at the bottom. Workers would then lift the iron, cut into it, and force slag in to oxidize what impurities remained. The iron was then broken up, remelted, and formed into a loup via hammering. The Lancashire Process reused heat from the flames to preheat air being pumped in by the bellows, making it more heat-efficient than the Walloon Process. [16]

Puddling

Puddling was a larger scale way to produce wrought iron than a finery that was able to use mineral coals instead of charcoal. To prevent impurities from the coal from contaminating the iron, puddling placed the coal in an adjacent chamber to the iron, where most of the heat reached the iron by reflecting off the ceiling. This is where the name "puddling" comes from. Puddlers could handle three times as much iron as a finer: 600 pounds at a time. Workers would push any solidifying clumps of iron under the surface of the molten mix so they wouldn't oxidize. After most of the impurities had oxidized, a worker would split the iron into three lumps, which would be pressed by a machine called a squeezer to press out the remaining liquid slag. [17]

Forging

Forging produced wrought iron using blooms and rods. Forging is effectively hammering. Large hammers between 50-400 pounds could be used; lighter hammers typically produced smaller things. Forging hammers were automated by waterwheel or steam power, and could strike up to 250 times per minute. [18]

The Furnace

The furnace was about 32-40 feet tall, with the upper portion in a conical shape. The walls had an inner and oughter layer, the outer was usually made of granite or slate, while the inner was usually made of sandstone or firebrick because of their durability to high temperatures. Between the two walls was an eight-inch space filled with stone chips or broken cinderblocks. This space allowed the inner wall to expand and contract comfortably without bursting the outer wall. The area where workers would empty wheelbarrows full of iron ore was called the trunnel head or throat, and the opening above the hearth of the shaft below the trunnel head was called the bosh, which supported the furnace burden while funneling the molten slag. [19] The taper of the shaft, bosh and crucible was entirely dependent on the type of ore smelted, charcoal quality, and what iron was desired as the finished product. In the United States a straight, uniform 40-50 foot stack was needed as hydrates and oxides of iron were smelted. Heat-exchanges or hot blast stoves were installed in the 19th century to increase efficiency. By the early 20th century, the iron furnaces were forced to change due to the moving times, they grew to be about 80 feet tall, the shape and proportion of the hearth and bosh and the addition of a belllhopper to the trunnel head allowed for the use of new materials. [20]


Notes

  1. ↑ McVarish, D.C. 2008, p. 259.
  2. ↑ McVarish, D.C. 2008, p. 259.
  3. ↑ McVarish, D.C. 2008, p. 259.
  4. ↑ McVarish, D.C. 2008, p. 260.
  5. ↑ McVarish, D.C. 2008, p. 266.
  6. ↑ McVarish, D.C. 2008, p. 259.
  7. ↑ McVarish, D.C. 2008, p. 259.
  8. ↑ McVarish, D.C. 2008, p. 260.
  9. ↑ McVarish, D.C. 2008, p. 262.
  10. ↑ Straka, T.J. 2014, p. 104.
  11. ↑ Straka, T.J. 2014, p. 105.
  12. ↑ McVarish, D.C. 2008, p. 259.
  13. ↑ McVarish, D.C. 2008, p. 260.
  14. ↑ McVarish, D.C. 2008, p. 260-265.
  15. ↑ McVarish, D.C. 2008, p. 268.
  16. ↑ McVarish, D.C. 2008, p. 268-269.
  17. ↑ McVarish, D.C. 2008, p. 270.
  18. ↑ McVarish, D.C. 2008, p. 271.
  19. ↑ McVarish, D.C. 2008, p. 266.
  20. ↑ McVarish, D.C. 2008, p. 267.

References

  • Straka, T. J. (2014). Historic Charcoal Production in the US and Forest Depletion: Development of

Production Parameters. Advances in Historical Studies, 3, 104-114. http://dx.doi.org/10.4236/ahs.2014.32010

  • McVarish, Douglas C. 2008. American Industrial Archaeology: A Field Guide. Walnut Creek, Calif.: Left Coast Press, Inc.
Retrieved from "https://wiki.ironallentownpa.org/index.php?title=Iron_production&oldid=142"