Cast House at Hopewell Furnace National Historic Site

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Historical Furnace Village Main Page

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An iron furnace is essentially a large chimney that is loaded with raw materials from the top, and finished materials—molten iron in this case—come out at the bottom. At the top, workers called fillers constantly fill the furnace with repeated layers of charcoal, ore, and flux via the charging hole. (Flux is a mineral such as limestone that causes the waste materials in the ore to collect together like metal to a magnet.) When ready, the furnace is lit and large amounts of air are blown into it to create a temperature of over 2,800º F. This heat melts the ore and flux, and the molten iron and waste materials called slag collect at the bottom of the furnace. Because the slag is lighter than iron, it floats on top and can easily be removed.

At the bottom level of the furnace is the cast house, a building that keeps the furnacemen and other employees, as well as equipment, out of the rain and snow. A couple times each day, the furnaceman releases the molten iron and slag by tapping the furnace, which is commonly done by punching a hole in or removing the refractory clay that plugs the exit. When the furnace is taped, a bell at the top of the cast house is rung to alert the moulders (British version of molder), the men who create the molds into which the molten ore is poured to produce cast iron shapes. All the work is done in the cast house.

Up until 1844, Hopewell Furnace produced consumer goods such as pots, pans, tools, and stoves (which the company was most famous for). All such products required molds. After 1844, the furnace mainly produced pig iron, which were iron bars that were sent to refinery forges that converted them into consumer goods. Molds were not needed for pig iron. Instead, small trenches were dug into the dirt in front of the furnace, and when it was taped, the liquid iron flowed into the trenches and formed long bars. The photo below is of a stack of pig iron bars outside the cast house.

Pig iron bars outside the Cast House at Hopewell Furnace National Historic Site

Illustration of how pig iron bars were made

The cast house now standing at Hopewell Furnace National Historic Site is a modern reproduction built in 1965 by the National Park Service. The original cast house was built in 1771 when the furnace opened, and it remained in use until the furnace closed in 1883. After that, the building slowly rotted away until nothing was left but the foundation. There are photos of the original, so the National Park Service was well aware of what the cast house looked like.

1887 photo of the Hopewell Furnace Cast House

Excavations of the site in 1962-63 led archeologists to the conclusion that the original 1771 cast house was much smaller than the one standing in 1883, which makes sense because the operation was much bigger by then (peak production was from 1820 to 1840). What the National Park Service ultimately built was a cast house that might have been standing in 1840, though exactly what the cast house looked like at that time is not known for certain.

Cast House at Hopewell Furnace National Historic Site

The first area visitors come to when entering the cast house is the hearth of the furnace itself. This is where the molten iron exits the furnace when it is tapped.

Hearth of the iron furnace at Hopewell Furnace National Historic Site

Much of the cast house today is set up for visitors to create their own wet sand molds, known as flask casting. These demonstrations are held Wednesdays through Sundays starting around Memorial Day and continuing through Labor Day. There is no cost to attend. For a schedule, see the National Park Service’s Calendar web page for Hopewell Furnace National Historic Site. In the KEYWORD search box, enter MOLDING. Once a month the Rangers melt aluminum in a barrel furnace and actually pour the metal into molds (search ALUMINUM CASTING DEMONSTRATION).

Flask Casting demonstration area inside the Cast House at Hopewell Furnace National Historic Site

Aluminum casting demonstration at Hopewell Furnace National Historic Site (photo by National Park Service)

Large bellows (replaced by blowing tubs at Hopewell Furnace in 1822) blew air into the furnace to fuel the fire. The air was “room temperature” so to speak, and furnaces that used room temperature air were called cold-blast furnaces. Starting in 1825, furnaces began using pre-heated air. Called hot-blast, this technology used less fuel and created higher temperatures and could thus produce iron cheaper than cold-blast furnaces. By the mid-1830s, hot-blast furnaces that used anthracite coal instead of charcoal were noticeably chipping away at the sales of iron and the iron products produced at cold-blast furnaces. The owners of Hopewell Furnace actually built a hot-blast anthracite coal furnace in 1853, but the cost of shipping coal to Elverson far outweighed any benefits of the hot-blast technology. The furnace was shut down just four years later. Eventually, even the cold-blast furnace closed for good (1883). The last cold-blast furnace in the United States, the Pleasant Furnace in Curtin, Pennsylvania, closed in 1921.

The water wheel on the side of the cast house (also a reconstruction by the National Park Service) supplied the power to run the massive bellows / blowing tubs. The water came from the surrounding creeks and was carried to the water wheel via a 1-mile long flume (aka headrace). The water picked up speed as it ran downhill, and when it emptied out at the water wheel, it hit the buckets (paddles) of the wheel with a force strong enough to make it spin (think of blowing air into a pinwheel). You can view the flume from the Bridge House above the cast house or by walking around the back of the cast house. The water exited the water wheel via a tailrace that emptied into French Creek.

Headrace carried water to the Hopewell Furnace water wheel from the surrounding creeks, Hopewell Furnace National Historic Site

Water exited the Hopewell Furnace water wheel via the tailrace and emptied into French Creek, Hopewell Furnace National Historic Site

To power bellows, the wheel is connected to a shaft. As it spins, iron cams attached to the shaft trip levers that cause the bellows to expand and fill with air, then contract and blow the air into the furnace. When the blowing tubs were installed (on top of the water wheel in the photo below), piston rods attached to each end of the water wheel shaft moved the pistons inside the tubs to compress the air, forcing it through a pipe that was connected to the furnace. Water wheel technology was eventually replaced in the mid-1800s by stream driven turbines, though at Hopewell Furnace the water wheel was used the entire time. The current wheel was installed in 2006 by the National Park Service. This is the fifth wheel installed since the park opened in 1938. Water and wood do not mix well, so repairs and replacements of water wheels were common.

Water wheel at Hopewell Furnace National Historic Site

Blast pipe carried air into the furnace, Hopewell Furnace National Historic Site

There is a room inside the cast house with a display of products made at Hopewell Furnace. There is a completed stove as well as cast iron plates used to make a stove. In another area is a large pile of stove plates. The first stoves at Hopewell Furnace were 6-plate stoves (comprised of 6 iron plates), but these were eventually replaced by 10-plate stoves. Most furnace companies did not assemble the stoves. Instead, the plates were shipped to stove dealers who put them together. Dealers could pay extra to have the furnaces cast plates with their company names on them or plates with custom designs.

Room inside the Cast House at Hopewell Furnace National Historic Site with examples of products made at Hopewell Furnace

10-plate stove cast at Hopewell Furnace

Stove plates on display inside the Cast House at Hopewell Furnace National Historic Site

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