From Iron Ore To Engines

| September/October 1996

3982 Bollard Avenue Cincinnati, Ohio 45209

Although much has been written about engines, comparatively little had been reported about the iron and steel used in their construction. This article seeks to remedy that situation.

Today's chemistry and physics surpass what was known in the late 1800s and the earliest years of the twentieth century. All the same, the designers and builders of boilers and engines had amassed an impressive array of scientific facts and formulas. This essay presents the story of steel and iron as it would have been told around 1900.(In other words, take heed! A few of the 'facts' may not be facts anymore.)

In the last decade of the nineteenth century, publishers brought out several textbooks for mechanical engineers to follow in taking advanced college courses and in working for companies which built engines. These weighty tomes provide a historical record of what was deemed of utmost importance for students and practitioners of engineering to know at the height of the industrial era. Such books devote numerous chapters to descriptions of iron and steel. Apparently, the term 'iron' served as (a) a generic classification for a wide range of metallic alloys including steel, (b) a more specific designator of certain metals which differed from steel in molecular structure and (often) in manner of production, and (c) the very specific signifier of the silvery-white, malleable, ductile element symbolized by Fe. With meanings from general to specific, 'iron' in old textbooks can be, and occasionally is, a highly ambiguous word.

Despite such confusing terminology, the engineering books from around the turn of the century provided much useful instruction to readers born not long after the Civil War. Most begin their treatment of the subject of iron by examining the nature of stresses, both longitudinal and transverse. Under the former heading belong tensile stress, which resists a pulling force, and compression, which resists a crushing force. Beneath transverse stresses may be classified (a) shearing stress, which resists cutting across, (b) bending stress, which resists breaking across, and (c) torsional stress, which resists twisting (Thurston 46). Knowledge of such forces enabled engineers to design stronger boilers and engines. With stress as a force acting upon a structure, strain, according to Robert H. Thurston, was the resultant change of structural form (47). Unfortunately, general agreement on such a seemingly simple matter as defining 'stress' and 'strain' could not be reached:

An external force applied to a body, so as to pull it apart, is resisted by an internal force, or resistance, and the action of these forces causes a displacement of the molecules, or deformation. By some writers the external force is called a stress, and the internal force is a strain; others call the external force a strain, and the internal force a stress: this confusion of terms is not of importance, as the words stress and strain are quite commonly used synonymously, but the use of the word strain to mean molecular displacement, deformation, or distortion, as is the custom of some, is a corruption of the language. (Kent 236)