The Steel Business: The Open-Hearth Furnace
By the turn of the century, most of Carnegie's steel came from vast brick ovens called open-hearth furnaces. They were the future of steel-making. In 1890 at Homestead, the world's largest open-hearth mill, 16 furnaces ran-each producing forty tons of steel every six hours.
Open-hearth furnaces produced terrific heat and used the waste gases of the molten iron to generate even more heat, nearly 3,000 degrees. Fires blazed at both sides of the hearth, passing heated currents of air and gas alternately from each fire over the molten iron. The waste gas passed into chambers above the two fires, trapping heat in special firebrick and making the next flow of gas even hotter. The extreme heat eventually burned out the impurities in the iron, resulting in silvery white steel.
Before the furnace was tapped and the steel poured out, workers banged on beams to warn others to take cover. "Jesus, it was hot," recalled a worker. "If there was water in the molds when they would tap it, the damn thing would explode and metal would fly all over the area."
The steel was finished by adding carbon and manganese-not as simple as it sounds. In 1919 an open-hearth worker described the process in his diary: "You lift a large sack of coal to your shoulders, run towards the white hot steel in a hundred-ton ladle, must get close enough without burning your face off to hurl the sack, using every ounce of strength, into the ladle and run, as flames leap to roof and the heat blasts everything to the roof. Then you rush out to the ladle and madly shovel manganese into it, as hot a job as can be imagined."
By the middle of the 20th century, the open-hearth process was surpassed by other technologies. The last open-hearth furnaces in North America were bricked up in the 1980s.