|How Iron Is Made|
FOLPI Ironmaking Demonstration, June, 2002
Mined from the Earth and melted from the rock around it, iron has been molded and hammered for countless purposes for thousands of years. At the Long Pond ironworks, the forges and blast furnaces built between 1766 and 1882 illustrate the technological advances that took place in the ironmaking process over the course of some 120 years.
Throughout Long Pond's history, the Wanaque River was harnessed to turn the waterwheels. The wheels powered huge bellows (or later, piston blowing engines) that blasted air into the furnaces, intensifying the fire. In addition, magnetite iron ore was mined locally and the forests were harvested to make charcoal to fuel the furnaces.
To make the charcoal, colliers prepared a mound of cut timber sealed with mud and leaves, set the mound on fire, and fired the wood slowly, as in a kiln, for days. Limestone was also obtained from nearby quarries to be used in the furnaces as a fluxing agent-that is, to create the chemical reaction that separated the iron from the ore.
Blast furnaces operated 24 hours a day, seven days a week, for as many months of the year as possible. Men loaded the ore, charcoal and limestone into the top of the furnace; inside, the raw materials were heated to a temperature of about 2,500 degrees Fahrenheit. Under these conditions, the mixture separated into molten iron and a blend of waste material called "slag." Being heavier, the molten iron sank to the bottom of the hearth, where it was "tapped," or channeled out of the furnace into sand beds raked in the casting-house floor, where they cooled to form "pigs," or bars of iron.
Long Pond's first blast furnace, built in 1766, was about 25 feet tall; the site's Civil War-era furnaces, built about 100 years later, reached a height of 65 feet. Colonial-era charcoal furnaces were capable of producing up to 30 tons of bar iron a month; the much larger furnaces of the 19th century, such as those at Long Pond, had a substantially higher output.
In addition to blast furnaces, forges were used at Long Pond in the ironmaking process. The forges contained huge trip hammers, also operated with waterwheels, that beat bar iron to remove impurities, strengthening and shaping the metal. Additionally, hearths in the forge could be used to smelt small quantities of iron; the iron was then reheated in order to manufacture finished products.
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