Cornwall Iron Furnace
Encyclopedia
Cornwall Iron Furnace is a designated National Historic Landmark
that is administered by the Pennsylvania Historical and Museum Commission
in Cornwall
, Lebanon County
, Pennsylvania
in the United States
. The furnace was a leading Pennsylvania iron
producer from 1742 until it was shut down in 1883. The furnaces, support buildings and surrounding community have been preserved as a historical site and museum, providing a glimpse into Lebanon County's industrial past. The site is the only intact charcoal-burning iron blast furnace in its original plantation in the western hemisphere. Established by Peter Grubb in 1742, Cornwall Furnace was operated during the Revolution by his sons Curtis
and Peter Jr.
who were major arms providers to George Washington. Robert Coleman acquired Cornwall Furnace after the Revolution and became Pennsylvania's first millionaire
. Ownership of the furnace and its surroundings was transferred to the Commonwealth of Pennsylvania in 1932.
, four bloomeries
, six steel furnaces, three slitting mills, two plate mills, and one wire mill in operation in Colonial Pennsylvania.
The furnaces at Cornwall Furnace went through two stages of technology. Peter Grubb was born in Delaware about 1702 and settled in what is now Lebanon County in 1734. He bought about 300 acres (1.2 km²) of magnetite
rich land. Grubb also noticed that his land had the other natural resources needed to produce iron. Namely, vast stands of timber
for the production of charcoal
, running water to operate the bellows, and an ample supply of limestone needed to add flux to the smelting furnaces. Grubb's plans were further helped by the fact that the magnetite at Cornwall was either very close to or on the surface of his land. He was ready to venture into the iron business and set about the task of building an iron "plantation". These centers of iron production were usually located well away from the heavily cleared farmlands and were nestled in the Ridge and Valley section of Pennsylvania. Grubb constructed his furnaces, first a bloomery and later the more modern charcoal-fired blast furnace and the support buildings and mill village
that was needed to house his workers. He named his operation Cornwall because his father, John Grubb had come from Cornwall, UK in 1677. Cornwall Iron Furnace was an excellent fit for the agricultural based economy of the Thirteen Colonies
. Iron was needed to make into tools, nails and weapons. The official policy of Great Britain frowned on manufacturing in the colonies, but England
was no longer able to produce the needed iron for its needs let alone the needs of the colonists. In fact England had become dependent on import
ing iron from Sweden
.
Peter Grubb was not really an ironmaster, but a builder. In 1745 he leased the ironworks to a consortium, Cury and Company, for 25 years and returned to Wilmington. The consortium continued the operation, with ownership passing to Peter's sons, Curtis
and Peter Jr.
, after his death in 1754. The brothers took over the operation in 1765 and ran it quite successfully until the late 1780's. Curtis operated the Cornwall Furnace and lived on site; c1773 he built the original 19 rooms of the mansion that still stands prominently next to the property. Peter Jr. ran a forge at Hopewell
, refining the pig iron produced by the furnace into more valuable bar iron. The ironworks were major suppliers to the Revolutionary War effort, and George Washington
once visited to inspect the operation. Unfortunately for the Grubb family, as described in Curtis Grubb's biography
, they were unable to retain control of the operation after Curtis' marriage in 1783. Most of the Grubb's holdings gradually fell into the hands of Robert Coleman, culminating in 1798. Coleman's son, William, was named manager of Cornwall Furnace and lived in the mansion; in 1865 the Colemans remodeled it into the 29 room structure known today as Buckingham Mansion.
) in colonial America, but to restrict their manufacture there into finished iron goods. Existing manufacturing works could continue, but new ones for certain processes were prohibited.
. Grubb built this in 1737 to test the market value of his ore. It was an economical way to test the market without having to invest in building the much more efficient and profitable blast furnace.
A bloomery is basically an enlarged blacksmith
's hearth. It consists of a pit or chimney
with heat-resistant walls made of earth, clay, or stone. (Sandstone
was used at Cornwall.) Near the bottom, one or more clay pipes enter through the side walls. These pipes, called tuyere
s, allow air to enter the furnace, either by natural draft or by forced with a bellow
s. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the bottom.
The first step taken before the bloomery can be used is the preparation of the charcoal
and the iron ore. The charcoal is produced by heating wood to produce the nearly pure carbon fuel needed for the refining process. The ore is broken into small pieces and roasted in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed. Since slag from previous blooms may have a high iron content, slag from previous blooms can be broken up and recycled into the bloomery with the new ore.
In operation, the bloomery is preheated by burning charcoal, and once hot, iron ore and additional charcoal are introduced through the top, in a roughly one to one ratio. Inside the furnace, carbon monoxide
from the incomplete combustion of the charcoal reduces
the iron oxides in the ore to metallic iron, without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. Since the desired product of a bloomery is easily forgeable, nearly pure iron, with a low carbon
content, the temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing the carbon and becoming unforgeable. Limestone
could also be added to the bloomery, about 10% of the ore weight, which would act as flux
and help carry away impurities.
The small particles of iron produced in this way fall to the bottom of the furnace and become welded together to form a spongy mass of the bloom. The bottom of the furnace also fills with molten slag, often consisting of fayalite
, a compound of silicon
, oxygen and iron mixed with other impurities from the ore. Because the bloom is highly porous, and its open spaces are full of slag, the bloom must later be reheated and beaten with a hammer to drive the molten slag out of it. Iron treated this way is said to be wrought, and the resulting nearly pure iron wrought iron
.
. The blast furnace burned hotter than the bloomery and was able to render molten pig iron
("charcoal iron"
) from the ore.
A blast furnace relies on the fact that the unwanted silicon
and other impurities are lighter than the molten iron that is the main product. Grubb's furnace was built in the form of a tall chimney
-like structure lined with refractory
brick. Charcoal
, limestone
and iron ore (iron oxide) were poured in at the top, and air was blown in through tuyeres near the base. The resulting "blast" promotes combustion of the charcoal (more modern furnaces use coke
or even anthracite), creating a chemical reaction that reduces the iron oxide to the base metal which sinks to the bottom of the furnace. The exact nature of the reaction is:
Fe
2O
3 + 3 C
O
→ 2Fe + 3CO2
More precisely, the compressed air blown into the furnace reacts with the carbon in the fuel to produce carbon monoxide
, which then mixes with the iron oxide
, reacting chemically to produce iron and carbon dioxide
, which leaks out of the furnace at the top. In the beginning of the reaction cycle, the hot blast, also called "wind", containing pre-heated gas from Cowper stoves and air, is blasted into the furnace through tuyeres. The wind will ignite the coke and the Boudouard reaction
will take place:
C + O2 → CO2
CO2 + C → 2 CO
The temperature in the furnace typically runs at about 1500 °C, which is enough to also decompose limestone
(calcium carbonate
) into calcium oxide
and additional carbon dioxide:
CaCO3 → CaO + CO2
The calcium oxide reacts with various acidic impurities in the iron (notably silica), forming a slag containing calcium silicate
, Ca
Si
O
3 which floats on the iron.
The pig iron produced by the blast furnace is not useful for most purposes due to its high carbon content, around 4-5%, making it very brittle
. Some pig iron is used to make cast iron goods, often being remelted in a foundry cupola.
For other purposes further processing is needed to reduce the carbon content to enable iron to be used for tools or as a construction material. There have been various processes for this. The earliest process was conducted in the finery forge
. In the late 18th century, this began to be displaced by 'potting and stamping', but the most successful new process of the industrial revolution
period was puddling
.
This is now done by forcing a jet of high-pressure oxygen into a special rotating container containing the pig iron. Some of the carbon is oxidised into carbon monoxide
, CO, and carbon dioxide, CO2. This also oxidizes impurities in the pig iron. The container is rotated and the processed pig iron can be separated from the oxidised impurities. Before the mid 19th century, pig iron from the blast furnace was made into wrought iron
, which is commercially pure iron. At that period, if steel was needed, particularly pure varieties of iron were heated with charcoal in a cementation furnace to produce blister steel (with about 1-2% carbon). This might be further purified using the crucible technique, but steel was too expensive to use on a large scale. However with the introduction of the Bessemer process
in the late 1850s and then other processes, the production of steel was dramatically increased. By the late 19th century most iron was being converted to steel before use.
. The stack of wood was covered with leaves and dirt and was set on fire in the center. The fires were allowed to smolder for ten to fourteen days, under the careful, round the clock, supervision of the collier. The colliers were careful to make sure that enough heat was produced to expel moisture, tar and other substances from the wood without burning the wood up entirely. Wood was not charred until just before it was needed to keep it from getting wet and becoming useless. The demand for charcoal was so tremendous that Cornwall Furnace used an entire acre of wood every day for making charcoal. http://www.phmc.state.pa.us/ppet/cornwall/page1.asp?secid=31
Such a massive and difficult iron and charcoal making operation need a massive and hardened workforce
. The furnace alone needed as many as sixty people working around the clock in twelve hour shifts. The iron works support staff included a company clerk, a host of teamster
s, woodcutters, the colliers, farmers and household servants. There was a wide gap between the classes. Workers were housed in small homes and worked very hard for low wages. The owners and supervisors of the furnace lived in mansions with sizable servant staffs. Historians have likened life at the furnace to life in a feudal barony.
There were three groups of workers at Cornwall Iron Furnace: Free labor, indentured servant
s and slaves. Slavery was legal in Pennsylvania until it was gradually abolished beginning in 1780 when the importation of slaves was prohibited. The management of the furnace had quite a bit of trouble with the staff of indentured servants. These unskilled workers were imported from Germany
, England
and Ireland
. Many of them worked at Cornwall for a short time before eventually running away.
's office in Philadelphia
to bookkeeper at Cornwall Iron Furnace to becoming Pennsylvania's first millionaire. http://www.phmc.state.pa.us/ppet/cornwall/page4.asp?secid=31
Coleman arrived in Philadelphia from Ireland in 1764. After serving as a clerk and bookkeeper he went on to acquire a lease on Salford Forge near Norristown
in 1773 and immediately made a sizeable profit by manufacturing cannonballs
and shot at Salford and Elizabeth Furnaces. He then used his profits to purchase a two thirds share of Elizabeth Furnace, shares of Cornwall and the Upper and Lower Hopewell Furnaces, (not the similarly named Hopewell Furnace), and ownership of Speedwell Forge
. Soon Coleman was able to construct Colebrook Furnace, purchase the rest of Elizabeth Furnace and acquired 80% ownership of Cornwall Furnace and the ore mines nearby. His business acquisitions and the profits turned from them enabled him to become the first millionaire in the history of Pennsylvania.
George oversaw many improvements in production at Cornwall Iron Furnace. The bellows were replaced with "blowing tubs". The blowing tubs were piston-powered air pumps and containers that held compressed air and forced that air into the furnaces. The waterwheel was replaced by a steam engine in 1841. And the furnace stack was rebuilt in the 1850s.
The Colemans turned direct supervision of Cornwall Iron Furnace to John F. Reynolds
in 1848. He was a graduate of West Point
and managed the furnace until the outbreak of the Civil War. Reynolds was commissioned a general
and was the first Union General to fall at the Battle of Gettysburg
.
."
processes of creating steel
, the replacement of charcoal with coke
and anthracite coal
, the discovery of iron deposits at the Iron Range
in Minnesota
near Lake Superior
, and the building of modern factories in Pittsburgh
, Steelton
and Bethlehem
brought about the end of iron production in Cornwall. Cornwall Furnace no longer earned a profit
in its last ten years of operation and the last owner, Robert Habersham Coleman, had it shut down on February 11, 1883. In 1932, the furnace and ancillary buildings were deeded by Margaret Coleman Buckingham and have since been restored and open to the public.
National Historic Landmark
A National Historic Landmark is a building, site, structure, object, or district, that is officially recognized by the United States government for its historical significance...
that is administered by the Pennsylvania Historical and Museum Commission
Pennsylvania Historical and Museum Commission
The Pennsylvania Historical and Museum Commission is the governmental agency of the Commonwealth of Pennsylvania responsible for the collection, conservation and interpretation of Pennsylvania's historic heritage...
in Cornwall
Cornwall, Pennsylvania
Cornwall is a borough in Lebanon County, Pennsylvania, United States. It is part of the Lebanon, PA Metropolitan Statistical Area. The population was 3,486 at the 2000 census.-History:...
, Lebanon County
Lebanon County, Pennsylvania
As of the census of 2000, there were 120,327 people and 32,771 families residing in the county. The population density was 332 people per square mile . There were 49,320 housing units at an average density of 136 per square mile...
, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The furnace was a leading Pennsylvania iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
producer from 1742 until it was shut down in 1883. The furnaces, support buildings and surrounding community have been preserved as a historical site and museum, providing a glimpse into Lebanon County's industrial past. The site is the only intact charcoal-burning iron blast furnace in its original plantation in the western hemisphere. Established by Peter Grubb in 1742, Cornwall Furnace was operated during the Revolution by his sons Curtis
Curtis Grubb
Curtis Grubb , Patriot and oldest son of Peter and Martha Bates Grubb, was a second-generation member of the Grubb Family Iron Dynasty along with his younger brother Peter Jr...
and Peter Jr.
Peter Grubb, Jr.
Peter Grubb, Jr. , Patriot and second son of Peter and Martha Bates Grubb, was a second-generation member of the Grubb Family Iron Dynasty along with his older brother Curtis Grubb...
who were major arms providers to George Washington. Robert Coleman acquired Cornwall Furnace after the Revolution and became Pennsylvania's first millionaire
Millionaire
A millionaire is an individual whose net worth or wealth is equal to or exceeds one million units of currency. It can also be a person who owns one million units of currency in a bank account or savings account...
. Ownership of the furnace and its surroundings was transferred to the Commonwealth of Pennsylvania in 1932.
Overview
Cornwall Iron Furnace was one of many ironworks that were built in Pennsylvania over a sixty-year period, from 1716-1776. There were at least 21 blast furnaces, 45 forgesFoundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...
, four bloomeries
Bloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...
, six steel furnaces, three slitting mills, two plate mills, and one wire mill in operation in Colonial Pennsylvania.
The furnaces at Cornwall Furnace went through two stages of technology. Peter Grubb was born in Delaware about 1702 and settled in what is now Lebanon County in 1734. He bought about 300 acres (1.2 km²) of magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
rich land. Grubb also noticed that his land had the other natural resources needed to produce iron. Namely, vast stands of timber
Timber
Timber may refer to:* Timber, a term common in the United Kingdom and Australia for wood materials * Timber, Oregon, an unincorporated community in the U.S...
for the production of charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
, running water to operate the bellows, and an ample supply of limestone needed to add flux to the smelting furnaces. Grubb's plans were further helped by the fact that the magnetite at Cornwall was either very close to or on the surface of his land. He was ready to venture into the iron business and set about the task of building an iron "plantation". These centers of iron production were usually located well away from the heavily cleared farmlands and were nestled in the Ridge and Valley section of Pennsylvania. Grubb constructed his furnaces, first a bloomery and later the more modern charcoal-fired blast furnace and the support buildings and mill village
Mill Village
Mill Village may refer to:* Mill village, a settlement that developed around one or more mills or factories* Mill Village, Nova Scotia, Canada* Mill Village, Pennsylvania, United States-See also:* Mooresville Mill Village* Pepper Mill Village...
that was needed to house his workers. He named his operation Cornwall because his father, John Grubb had come from Cornwall, UK in 1677. Cornwall Iron Furnace was an excellent fit for the agricultural based economy of the Thirteen Colonies
Thirteen Colonies
The Thirteen Colonies were English and later British colonies established on the Atlantic coast of North America between 1607 and 1733. They declared their independence in the American Revolution and formed the United States of America...
. Iron was needed to make into tools, nails and weapons. The official policy of Great Britain frowned on manufacturing in the colonies, but England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
was no longer able to produce the needed iron for its needs let alone the needs of the colonists. In fact England had become dependent on import
Import
The term import is derived from the conceptual meaning as to bring in the goods and services into the port of a country. The buyer of such goods and services is referred to an "importer" who is based in the country of import whereas the overseas based seller is referred to as an "exporter". Thus...
ing iron from Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
.
Peter Grubb was not really an ironmaster, but a builder. In 1745 he leased the ironworks to a consortium, Cury and Company, for 25 years and returned to Wilmington. The consortium continued the operation, with ownership passing to Peter's sons, Curtis
Curtis Grubb
Curtis Grubb , Patriot and oldest son of Peter and Martha Bates Grubb, was a second-generation member of the Grubb Family Iron Dynasty along with his younger brother Peter Jr...
and Peter Jr.
Peter Grubb, Jr.
Peter Grubb, Jr. , Patriot and second son of Peter and Martha Bates Grubb, was a second-generation member of the Grubb Family Iron Dynasty along with his older brother Curtis Grubb...
, after his death in 1754. The brothers took over the operation in 1765 and ran it quite successfully until the late 1780's. Curtis operated the Cornwall Furnace and lived on site; c1773 he built the original 19 rooms of the mansion that still stands prominently next to the property. Peter Jr. ran a forge at Hopewell
Hopewell (on Hammer Creek)
Hopewell is where Peter Grubb, who founded Cornwall, Pennsylvania in 1737, first began his iron making activities about 1739. It is an area about six miles southeast of Cornwall, in Lancaster County...
, refining the pig iron produced by the furnace into more valuable bar iron. The ironworks were major suppliers to the Revolutionary War effort, and George Washington
George Washington
George Washington was the dominant military and political leader of the new United States of America from 1775 to 1799. He led the American victory over Great Britain in the American Revolutionary War as commander-in-chief of the Continental Army from 1775 to 1783, and presided over the writing of...
once visited to inspect the operation. Unfortunately for the Grubb family, as described in Curtis Grubb's biography
Curtis Grubb
Curtis Grubb , Patriot and oldest son of Peter and Martha Bates Grubb, was a second-generation member of the Grubb Family Iron Dynasty along with his younger brother Peter Jr...
, they were unable to retain control of the operation after Curtis' marriage in 1783. Most of the Grubb's holdings gradually fell into the hands of Robert Coleman, culminating in 1798. Coleman's son, William, was named manager of Cornwall Furnace and lived in the mansion; in 1865 the Colemans remodeled it into the 29 room structure known today as Buckingham Mansion.
Iron Act
In American Colonial history, the Iron Act, passed in 1750, was part of the British legislation designed to encourage the production of raw materials (including pig ironPig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...
) in colonial America, but to restrict their manufacture there into finished iron goods. Existing manufacturing works could continue, but new ones for certain processes were prohibited.
Bloomery
The first furnace built by Peter Grubb at Cornwall Iron Furnace was a bloomeryBloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...
. Grubb built this in 1737 to test the market value of his ore. It was an economical way to test the market without having to invest in building the much more efficient and profitable blast furnace.
A bloomery is basically an enlarged blacksmith
Blacksmith
A blacksmith is a person who creates objects from wrought iron or steel by forging the metal; that is, by using tools to hammer, bend, and cut...
's hearth. It consists of a pit or chimney
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
with heat-resistant walls made of earth, clay, or stone. (Sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
was used at Cornwall.) Near the bottom, one or more clay pipes enter through the side walls. These pipes, called tuyere
Tuyere
A tuyere, also can be spelled as tuyère, is a tube, nozzle or pipe through which air is blown into a furnace or hearth.Air or oxygen is injected into a hearth under pressure from bellows or a blast engine or other devices...
s, allow air to enter the furnace, either by natural draft or by forced with a bellow
Bellow
- People :* Adam Bellow, vice president/executive editor at Collins Books* Alexandra Bellow , mathematician* Saul Bellow , American writer born in Canada of Russian-Jewish origin...
s. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the bottom.
The first step taken before the bloomery can be used is the preparation of the charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
and the iron ore. The charcoal is produced by heating wood to produce the nearly pure carbon fuel needed for the refining process. The ore is broken into small pieces and roasted in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed. Since slag from previous blooms may have a high iron content, slag from previous blooms can be broken up and recycled into the bloomery with the new ore.
In operation, the bloomery is preheated by burning charcoal, and once hot, iron ore and additional charcoal are introduced through the top, in a roughly one to one ratio. Inside the furnace, carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
from the incomplete combustion of the charcoal reduces
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
the iron oxides in the ore to metallic iron, without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. Since the desired product of a bloomery is easily forgeable, nearly pure iron, with a low carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
content, the temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing the carbon and becoming unforgeable. Limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
could also be added to the bloomery, about 10% of the ore weight, which would act as flux
Flux (metallurgy)
In metallurgy, a flux , is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time...
and help carry away impurities.
The small particles of iron produced in this way fall to the bottom of the furnace and become welded together to form a spongy mass of the bloom. The bottom of the furnace also fills with molten slag, often consisting of fayalite
Fayalite
Fayalite is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.Iron rich olivine is a relatively common constituent of acidic and...
, a compound of silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, oxygen and iron mixed with other impurities from the ore. Because the bloom is highly porous, and its open spaces are full of slag, the bloom must later be reheated and beaten with a hammer to drive the molten slag out of it. Iron treated this way is said to be wrought, and the resulting nearly pure iron wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...
.
Blast furnace
In 1742, Grubb replaced his bloomery with a 30 feet (9.1 m) high charcoal-fired cold blast furnaceCold blast
Cold blast, in ironmaking, refers to a furnace where air is not preheated before being blown into the furnace. This represents the earliest stage in the development of ironmaking...
. The blast furnace burned hotter than the bloomery and was able to render molten pig iron
Pig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...
("charcoal iron"
Charcoal iron
Charcoal iron is the substance created by the smelting of iron ore with charcoal.All ironmaking blast furnaces were fueled by charcoal until Abraham Darby introduced coke as a fuel in 1709. The more economical coke soon replaced charcoal in British furnaces, but in the United States, where timber...
) from the ore.
A blast furnace relies on the fact that the unwanted silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
and other impurities are lighter than the molten iron that is the main product. Grubb's furnace was built in the form of a tall chimney
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
-like structure lined with refractory
Refractory
A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
brick. Charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
, limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and iron ore (iron oxide) were poured in at the top, and air was blown in through tuyeres near the base. The resulting "blast" promotes combustion of the charcoal (more modern furnaces use coke
Coke
Coke may refer to:* Coca-Cola, a soft drink originally based on coca leaf extract** The Coca-Cola Company, makers of this drink** Cola, any soft drink similar to Coca-Cola** Soft drink, any non-alcoholic carbonated beverage* Coca, a plant...
or even anthracite), creating a chemical reaction that reduces the iron oxide to the base metal which sinks to the bottom of the furnace. The exact nature of the reaction is:
Fe
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
2O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
3 + 3 C
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
→ 2Fe + 3CO2
More precisely, the compressed air blown into the furnace reacts with the carbon in the fuel to produce carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
, which then mixes with the iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
, reacting chemically to produce iron and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, which leaks out of the furnace at the top. In the beginning of the reaction cycle, the hot blast, also called "wind", containing pre-heated gas from Cowper stoves and air, is blasted into the furnace through tuyeres. The wind will ignite the coke and the Boudouard reaction
Boudouard reaction
The Boudouard reaction is the redox reaction of a chemical equilibrium mixture of carbon monoxide and carbon dioxide at a given temperature. It is the disproportionation of carbon monoxide into carbon dioxide and graphite or its reverse:...
will take place:
C + O2 → CO2
CO2 + C → 2 CO
The temperature in the furnace typically runs at about 1500 °C, which is enough to also decompose limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
(calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
) into calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
and additional carbon dioxide:
CaCO3 → CaO + CO2
The calcium oxide reacts with various acidic impurities in the iron (notably silica), forming a slag containing calcium silicate
Calcium silicate
Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and sometimes formulated 2CaO.SiO2. It is one of group of compounds obtained by reacting calcium oxide and silica in various ratios e.g. 3CaO.SiO2, Ca3SiO5; 2CaO.SiO2, Ca2SiO4; 3CaO.2SiO2, Ca3Si2O7 and...
, Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
Si
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
3 which floats on the iron.
The pig iron produced by the blast furnace is not useful for most purposes due to its high carbon content, around 4-5%, making it very brittle
Brittle
A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...
. Some pig iron is used to make cast iron goods, often being remelted in a foundry cupola.
For other purposes further processing is needed to reduce the carbon content to enable iron to be used for tools or as a construction material. There have been various processes for this. The earliest process was conducted in the finery forge
Finery forge
Iron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge....
. In the late 18th century, this began to be displaced by 'potting and stamping', but the most successful new process of the industrial revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
period was puddling
Puddling (metallurgy)
Puddling was an Industrial Revolution means of making iron and steel. In the original puddling technique, molten iron in a reverberatory furnace was stirred with rods, which were consumed in the process...
.
This is now done by forcing a jet of high-pressure oxygen into a special rotating container containing the pig iron. Some of the carbon is oxidised into carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
, CO, and carbon dioxide, CO2. This also oxidizes impurities in the pig iron. The container is rotated and the processed pig iron can be separated from the oxidised impurities. Before the mid 19th century, pig iron from the blast furnace was made into wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...
, which is commercially pure iron. At that period, if steel was needed, particularly pure varieties of iron were heated with charcoal in a cementation furnace to produce blister steel (with about 1-2% carbon). This might be further purified using the crucible technique, but steel was too expensive to use on a large scale. However with the introduction of the Bessemer process
Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly...
in the late 1850s and then other processes, the production of steel was dramatically increased. By the late 19th century most iron was being converted to steel before use.
Charcoal
The blast furnaces at Cornwall Furnace needed a tremendous amount of charcoal in order to keep them fired and thereby create a steady production of iron. The making of the charcoal became an industry in itself. Hardwood trees were chopped down, dried, stacked and fired in 30 to 40 ft (9.1 to 12.2 m) pits. A collier carefully stacked the wood around a chimneyChimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
. The stack of wood was covered with leaves and dirt and was set on fire in the center. The fires were allowed to smolder for ten to fourteen days, under the careful, round the clock, supervision of the collier. The colliers were careful to make sure that enough heat was produced to expel moisture, tar and other substances from the wood without burning the wood up entirely. Wood was not charred until just before it was needed to keep it from getting wet and becoming useless. The demand for charcoal was so tremendous that Cornwall Furnace used an entire acre of wood every day for making charcoal. http://www.phmc.state.pa.us/ppet/cornwall/page1.asp?secid=31
Working at the furnace
The furnace operated twenty four hours a day, seven days a week, except for when it was closed for repairs. Cornwall Iron Furnace was capable of producing 24 tons of iron a week. A large waterwheel powered the bellows. Carts loaded with charcoal passed to and fro between the coal barn and the furnace under a protective roof designed to keep the charcoal dry. Other wagons hauled the ore from the mine to the top of the furnace on the hillside. Workers then manually transported the charcoal and ore to the furnace. The guttermen worked at the base of the furnace. They raked the cooling sand and dug channels for the molten pig iron. Next, they stacked the bars of pig iron outside. The working conditions were very difficult. Temperatures inside the casting house reached as high as 160 °F (71 °C).Such a massive and difficult iron and charcoal making operation need a massive and hardened workforce
Workforce
The workforce is the labour pool in employment. It is generally used to describe those working for a single company or industry, but can also apply to a geographic region like a city, country, state, etc. The term generally excludes the employers or management, and implies those involved in...
. The furnace alone needed as many as sixty people working around the clock in twelve hour shifts. The iron works support staff included a company clerk, a host of teamster
Teamster
A teamster, in modern American English, is a truck driver. The trade union named after them is the International Brotherhood of Teamsters , one of the largest unions in the United States....
s, woodcutters, the colliers, farmers and household servants. There was a wide gap between the classes. Workers were housed in small homes and worked very hard for low wages. The owners and supervisors of the furnace lived in mansions with sizable servant staffs. Historians have likened life at the furnace to life in a feudal barony.
There were three groups of workers at Cornwall Iron Furnace: Free labor, indentured servant
Indentured servant
Indentured servitude refers to the historical practice of contracting to work for a fixed period of time, typically three to seven years, in exchange for transportation, food, clothing, lodging and other necessities during the term of indenture. Usually the father made the arrangements and signed...
s and slaves. Slavery was legal in Pennsylvania until it was gradually abolished beginning in 1780 when the importation of slaves was prohibited. The management of the furnace had quite a bit of trouble with the staff of indentured servants. These unskilled workers were imported from Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
and Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
. Many of them worked at Cornwall for a short time before eventually running away.
Robert Coleman
Robert Coleman rose from a holding clerkship at a prothonotaryProthonotary
The word prothonotary is recorded in English since 1447, as "principal clerk of a court," from L.L. prothonotarius , from Greek protonotarios "first scribe," originally the chief of the college of recorders of the court of the Byzantine Empire, from Greek protos "first" + Latin notarius ; the -h-...
's office in Philadelphia
Philadelphia, Pennsylvania
Philadelphia is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers. It is the fifth-most-populous city in the United States,...
to bookkeeper at Cornwall Iron Furnace to becoming Pennsylvania's first millionaire. http://www.phmc.state.pa.us/ppet/cornwall/page4.asp?secid=31
Coleman arrived in Philadelphia from Ireland in 1764. After serving as a clerk and bookkeeper he went on to acquire a lease on Salford Forge near Norristown
Norristown, Pennsylvania
Norristown is a municipality in Montgomery County, Pennsylvania, northwest of the city limits of Philadelphia, on the Schuylkill River. The population was 34,324 as of the 2010 census. It is the county seat of Montgomery County...
in 1773 and immediately made a sizeable profit by manufacturing cannonballs
Round shot
Round shot is a solid projectile without explosive charge, fired from a cannon. As the name implies, round shot is spherical; its diameter is slightly less than the bore of the gun it is fired from.Round shot was made in early times from dressed stone, but by the 17th century, from iron...
and shot at Salford and Elizabeth Furnaces. He then used his profits to purchase a two thirds share of Elizabeth Furnace, shares of Cornwall and the Upper and Lower Hopewell Furnaces, (not the similarly named Hopewell Furnace), and ownership of Speedwell Forge
Speedwell Forge
Speedwell Forge was built in 1760 in Elizabeth Township, Lancaster County, Pennsylvania. It operated continuously until 1854, when it closed as iron production moved west. The following are notes collected while researching the associated ironmaster's mansion for a National Historic Register...
. Soon Coleman was able to construct Colebrook Furnace, purchase the rest of Elizabeth Furnace and acquired 80% ownership of Cornwall Furnace and the ore mines nearby. His business acquisitions and the profits turned from them enabled him to become the first millionaire in the history of Pennsylvania.
George Dawson Coleman
George Dawson Coleman was the grandson of Robert Coleman and son of James Coleman. He controlled much of the Coleman iron fortune with his brother, Robert. George acquired greater control of the ore mines at Cornwall and was able to experiment with iron furnaces that were fueled by anthracite coal instead of coke. He also invested in the expanding railroad, and built houses, a school and church for his employees. He was much loved his community and went on to serve several times in the Pennsylvania State Legislature. (Several churches built by the Coleman family are still in existence in the area, and they are known as Coleman Chapels.)George oversaw many improvements in production at Cornwall Iron Furnace. The bellows were replaced with "blowing tubs". The blowing tubs were piston-powered air pumps and containers that held compressed air and forced that air into the furnaces. The waterwheel was replaced by a steam engine in 1841. And the furnace stack was rebuilt in the 1850s.
The Colemans turned direct supervision of Cornwall Iron Furnace to John F. Reynolds
John F. Reynolds
John Fulton Reynolds was a career United States Army officer and a general in the American Civil War. One of the Union Army's most respected senior commanders, he played a key role in committing the Army of the Potomac to the Battle of Gettysburg and was killed at the start of the battle.-Early...
in 1848. He was a graduate of West Point
United States Military Academy
The United States Military Academy at West Point is a four-year coeducational federal service academy located at West Point, New York. The academy sits on scenic high ground overlooking the Hudson River, north of New York City...
and managed the furnace until the outbreak of the Civil War. Reynolds was commissioned a general
General
A general officer is an officer of high military rank, usually in the army, and in some nations, the air force. The term is widely used by many nations of the world, and when a country uses a different term, there is an equivalent title given....
and was the first Union General to fall at the Battle of Gettysburg
Battle of Gettysburg
The Battle of Gettysburg , was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania. The battle with the largest number of casualties in the American Civil War, it is often described as the war's turning point. Union Maj. Gen. George Gordon Meade's Army of the Potomac...
.
Robert Habersham Coleman
Robert Habersham Coleman was the fourth and last generation scion of the Colemans. He shut the facility in 1883, opening new facilities for the company. In 1881, at the time he took over his family's business, Coleman was worth about seven million dollars. By 1889 he was estimated to be worth thirty million dollars. By 1893 the fortune had vanished. One of his homes, Cornwall Hall, was a "symbol of the rise, fame and decline of the "king" of Cornwall (Pennsylvania) during America's Gilded AgeGilded Age
In United States history, the Gilded Age refers to the era of rapid economic and population growth in the United States during the post–Civil War and post-Reconstruction eras of the late 19th century. The term "Gilded Age" was coined by Mark Twain and Charles Dudley Warner in their book The Gilded...
."
Downfall
Cornwall Iron Furnace became obsolete by the 1880s. The Bessemer and open-hearthOpen hearth furnace
Open hearth furnaces are one of a number of kinds of furnace where excess carbon and other impurities are burnt out of the pig iron to produce steel. Since steel is difficult to manufacture due to its high melting point, normal fuels and furnaces were insufficient and the open hearth furnace was...
processes of creating steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, the replacement of charcoal with coke
Coke (fuel)
Coke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous. While coke can be formed naturally, the commonly used form is man-made.- History :...
and anthracite coal
Anthracite coal
Anthracite is a hard, compact variety of mineral coal that has a high luster...
, the discovery of iron deposits at the Iron Range
Iron Range
The Iron Range is a region that makes up the northeastern section of Minnesota in the United States. "The Range", as it is known by locals, is a region with multiple distinct bands of iron ore...
in Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
near Lake Superior
Lake Superior
Lake Superior is the largest of the five traditionally-demarcated Great Lakes of North America. It is bounded to the north by the Canadian province of Ontario and the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan. It is the largest freshwater lake in the...
, and the building of modern factories in Pittsburgh
Pittsburgh, Pennsylvania
Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally, it anchors the largest urban area of Appalachia and the Ohio River Valley, and nationally, it is the 22nd-largest urban area in the United States...
, Steelton
Steelton, Pennsylvania
Steelton is a borough in Dauphin County, Pennsylvania, three miles southeast of Harrisburg. In 1900, 12,086 people lived here; in 1910, 14,246 people lived here; in 1920, 13,248 people lived here; and in 1940, 13,115 people lived here. The population was 5,858 at the 2000 census...
and Bethlehem
Bethlehem, Pennsylvania
Bethlehem is a city in Lehigh and Northampton Counties in the Lehigh Valley region of eastern Pennsylvania, in the United States. As of the 2010 census, the city had a total population of 74,982, making it the seventh largest city in Pennsylvania, after Philadelphia, Pittsburgh, Allentown, Erie,...
brought about the end of iron production in Cornwall. Cornwall Furnace no longer earned a profit
Profit (economics)
In economics, the term profit has two related but distinct meanings. Normal profit represents the total opportunity costs of a venture to an entrepreneur or investor, whilst economic profit In economics, the term profit has two related but distinct meanings. Normal profit represents the total...
in its last ten years of operation and the last owner, Robert Habersham Coleman, had it shut down on February 11, 1883. In 1932, the furnace and ancillary buildings were deeded by Margaret Coleman Buckingham and have since been restored and open to the public.
External links
- Cornwall Iron Furnace official site
- Cornwall Iron Furnace Photos
- Science Aid: Blast Furnace How iron is extracted, for high school level
- Blast Furnace animation
- How a Blast Furnace works Illustrated.
- Precursors of the Blast Furnace
- Extensive picture gallery about all methods of making and shaping of iron and steel in North America and Europe. In German and English.
- Blast Furnace Museum Radwerk IV
- Schematic diagram of blast furnace and Cowper stove
- ironfurnaces.com - a free wiki dedicated to preserving the history and location of historic blast iron furnaces
- Period pro and con debate on the Iron Act