A Cupola furnace – otherwise known as a blast furnace – takes a rather divergent approach to copper smelting as compared to the reverberatory process. Most notable is the fact that a cupola has no separate fire box, both the copper and fuel are combined together within a vertically oriented hearth. There’s also the significant difference in how air is utilized within the furnace. While a reverberatory furnace relies on a natural draft to fuel its firebox the cupola utilizes a large volume of forced air which is “blasted” into the hearth during the melting process. While some mining districts relied solely on these types of furnaces for smelting their ore, the Lake Superior district turned to these blast furnaces only intermittently to refine their copper-laden slag.
The blast furnace at the Quincy Smelting Works was a two-story monstrosity that took up a good portion of the Cupola building’s eastern half. Each of the building’s three floors catered to the furnace in a very specific capacity, starting with the first floor itself – known as the Cupola Floor. Here sat the business end of the cupola, and it was here that both molten copper and slag were removed from the furnace once the process was complete. The second floor – known as the charging floor – was were the cupola was loaded with both fuel and slag. Atop of it all was the bin loading floor, where the cupola’s various ingredients were loaded into storage bins to await the furnace’s charging.
Though no longer extant, the old cupola furnace at Quincy most likely looked something like this. Both the slag and fuel were loaded into the furnace from its top – accessible by the sliding loading door seen in the illustration. Air was blown into the entire structure from a surrounding air manifold powered by an attached blower (not shown). The air entered the hearth from its bottom through a series of openings known as tuyeres. At the bottom of the entire furnace was a tapping spout from which the molten copper would be drawn.
Here’s a front elevation of another typical cupola. At the bottom is a brick lined hearth, topped by the crucible in which the fuel and slag are mixed. A steel lined water jacket surrounds the crucible, insulating the furnace and helping to keep the room housing the furnace bearable. Feeding the crucible are a series of tuyeres through which air is forced into the furnace.
Here’s another view, this one from the side elevation. Alternating layers of slag, coal and limestone (as a fluxing agent) are loaded into the furnace from a set of large charging doors at its top. Air forced into the furnace help feed the fire and allow the crucible to reach high enough temperatures to melt the slag. A typical charge is about 20 tons, with roughly 40 percent of that being lime and 22 percent consisting of fuel.
After the melting process is completed, the copper and slag are drawn off by means of spigots along the furnace’s base. The slag from this furnace is less then 1 percent copper, and as such is dumped as waste. The copper matte is ladled into molds and shipped to the warehouse.
Quincy’s cupola furnace was located on the first and second floors of the Cupola Building. Here on the first floor the furnace was joined by its steam powered blower – which would have been housed in the room labeled as “engine room extension”. The rest of the room provided open space for the tapping and casting of copper from the furnace as well as a pair of tram elevators used to bring ingredients for the furnace up to the charging and bin floors.
Today the Cupola Furnace is long gone, most likely a victim of scrappers. In its place is nothing but empty space, littered with a collection of debris scattered about the floor.
Up above we could make out a large hole in the roof – most likely where the old cupola use to rise up into the upper floor. Up there would have been the charging floor, where the fuel and slag would have been loaded into the cupola. Today all we could make out is a large pile of debris that had fallen down from the collapsed roof.
Due to the collapsed roof and all together nastiness of the upper floors, we couldn’t risk making our way up there to check things out. If we had we would have found ourselves looking down a line of large steel bins in which coal, slag, and limestone would have been stored. We would have also seen the top half of the cupola, complete with loading doors at floor level.
Moving up another floor we would have found ourselves sitting atop of those mineral bins, surrounded by a labyrinth of tram tracks in the floor. Coming up through the center of the floor would have been the furnace’s smoke stack, while the elevated trestle from the nearby reverberatory furnace building makes its way into the building’s north-east corner. Those same tracks would have also been used to transport coal over to the neighboring boiler plant, on the west side of the building. A pair of tram elevators would have rounded out the offerings.
Speaking of those tram elevators, we were able to find one still intact – somewhat – in the front of the building. Peering into the darkness we could make out a large tram car – one of several that must have once been pushed throughout the smelting complex. The car was full of something, though I’m not sure if it was just some debris or some actual ingredient once used in the furnace.
Reaching in to look up the shaft I could make out very little – save the long cable once used to pull the tram platform up the shaft. From here the car would have been brought up to the mineral loading floor three stories up – either to go straight to the slag dump or to one of the furnaces mineral bins.
With nothing much else to see here, we made our way to the back of the building and to the waiting door of the attached engine house….
The Quincy Smelter is private property and is open to the public only during special Quincy Smelter Association’s tours and events.
To learn more about the Cupola Building and its history be sure to visit the Quincy Smelter Blog for their own virtual tour of the site.
To view more photos from the Quincy Smelter – including some awesome wide angle imagery – be sure to check out the Quincy Smelter Gallery at David Clark Photography!
And of course, if you have any photos of your own to contribute to the discussion, make sure to post them over at the Copper Country forum’s Quincy Smelter Thread.