The Scrantons initially intended to make and market pig iron alone. However, they soon decided to produce a smaller, finished product. In 1844, nail-making machinery was installed and a puddling mill constructed approximately one thousand yards above the furnaces along Roaring Brook. Nails were made from wrought iron plates. In order to convert their cast iron into wrought iron, the Scrantons built several reverberatory or puddling ovens.
Cast iron averages about four percent carbon content, while wrought iron has virtually none. It is the difference which makes cast iron hard and brittle and wrought iron soft and malleable. In a puddling oven, cast iron pigs were stacked in a slag-lined chamber and reduced to a semimolten state. The iron never came into direct contact with the burning fuel, because it would have absorbed more carbon. Instead, superheated air was drawn over the pigs. This caused them to belt initially and then, as carbon burned off, to form into large pasty balls or blooms.
Workmen periodically stirred the bloom with a long iron rod tipped with slag. This helped to release excess carbon and to mix in the iron silicate. It was the addition of iron silicate which gave wrought iron its characteristically fibrous texture. After two hours of puddling, the bloom was removed with tongs and taken to a squeezer, where excess slag was forced out in fiery spurts.
Once squeezed, the wrought iron ingot was reheated and passed between large rolls, which formed it into a desired shape. For nails, flat plates were rolled which could later be cut into nail rods. When in 1847, the company began rolling T rail, an ingot had to be passed some six times through various shaped rolls until the proper profile was achieved.
The power for the rolling mills came from a waterwheel, until 1847 when they installed one of the earliest steam engines in the valley to provide more stable power.
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