Later iron making on the Marquette Iron Range (Part 2)

The Collinsville Blast Furnace in 1888 is seen. (Photo courtesy of the Marquette Regional History Center)

MARQUETTE — Last week’s article discussed the early attempts at iron making on the Marquette Iron Range using bloomery forge technology. All four bloomery forges in the area had short lives, going out of operation by the end of the 1850s with an estimated total output of less than 15,000 tons of iron. None of the forges ever returned a profit to investors.

Following the failure of the bloomery forges, the area shifted to the relatively newer technology of blast furnaces. The first several included the Collins Experimental Furnace in Collinsville (1858); the Pioneer Furnace Stack No. 1 in Negaunee (1858); the Collins Furnace, also in Collinsville (1858), the Pioneer Furnace Stack No. 2, also in Negaunee (1859); Northern Furnace in Harvey (1860); Bancroft Furnace in Forestville (1861), and they were followed by more than 20 others across the U.P. over the next four decades.

The blast furnaces achieved higher temperatures and fully melted the iron while using less fuel. Bloomery forges required some 200-300 bushels of charcoal to produce one ton of iron blooms, while blast furnaces took approximately 125 bushels of charcoal to melt one ton of ore. With the ore, blast furnaces combined fuel (mainly charcoal but also coal or coke), flux (primarily limestone) and air introduced under pressure. Coke is a coal-based fuel with a high carbon content and few impurities. Like charcoal, it is made by heating coal or oil in the absence of air. Flux is a material used to catalyze desired reactions. It chemically bonds to unwanted impurities and reaction products making them easier to remove.

The blast furnace was charged (filled) from the top, allowing chemical reactions to take place throughout the furnace as the material fell downward. Liquid iron and slag accumulated in a hearth at the bottom of the furnace. Slag was the stony waste matter separated from the metal during the smelting process.

The slag consisted of the remnants of the limestone flux, ash from the charcoal and substances formed by the reaction of impurities in the ore with the flux. When melted, the slag formed is lighter than the molten iron and floats on top. A special opening or “notch” was present on the furnace and through it the slag was drawn off for disposal.

Next, the furnace would be “tapped” allowing the liquid metal to flow out into a sand-casting bed. The beds consisted of a central channel or runner, with many individual ingots at right angles. They were named sow and pigs due to the resemblance to a litter of piglets being nursed by a sow. When the metal had cooled and hardened, the pigs were simply broken from sow.

Pig iron, also known as cast or crude iron, was an intermediate product of the iron industry in the production of steel. It has a high carbon content, typically 3.8-4.7% along with silica and other impurities, which made it brittle and not useful directly as a material except for limited applications. Rather than carburizing bloomery iron, pig iron needed to be decarburized (removing carbon) to make usable steel. Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. As pig iron was intended for remelting, the uneven size of the ingots and the inclusion of small amounts of sand caused only insignificant problems considering the ease of casting and handling them.

At the same time the blast furnaces were being introduced, the opening of the Soo Locks lead to the shipment of unprocessed ore to furnaces in Ohio and Pennsylvania. It also allowed for the shipment of coal and coke into the Upper Peninsula, although this proved impractical and uneconomical. Many of the local blast furnaces went out of business quickly due to financial and/or mechanical issues but some continued operating until the 1920s. Even after the blast furnaces ceased operations, the mining and shipment of unprocessed ore continued.

By the 1950s, a century of mining had exhausted the higher quality ores. But there was still iron to be mined in the Marquette Iron Range in the form of taconite. A poorer ore, taconite is an iron-bearing sedimentary rock that generally contains 30-35% iron and around 45% silica in the form of quartz, chert, or carbonate. With this shift came a change from underground mining to open pits such as the Empire and Tilden Mines.

In 1956, Cleveland Cliffs Iron Company pioneered the process of beneficiation which converted the low-grade ore to iron pellets. After the rock is crushed, the ore is separated from the worthless silica. Next it is mixed with a binder (bentonite clay) and rolled into three-eighths-inch pellets. The ore that was originally 39% iron at the Tilden Mine and 28% iron at the Empire Mine was transformed to 60% iron in pellet form.

As time and technology progressed the Marquette Iron Range continued producing larger and larger amounts of iron each year. From 500 tons shipped in 1853; by 1861, the output was 120,000 tons. In 1868, annual figures had reached half a million tons; and, by 1873, the range produced over one million tons of ore, a figure that steadily increased throughout the next century. The peak finally came in 1974 when 20 million tons of ore and high-grade pellets were shipped from the Upper Peninsula.

Since then, production has dwindled. Of the dozens of iron mines that dotted the Marquette Iron Range over the last 170 years, today only the Tilden is still operating. Some unmined iron deposits remain, most notably under the village of Palmer. It remains to be seen if it will ever be economically viable enough to move the village in order to continue mining.


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