Biographical / Historical
Tadeusz Sendzimir, a Polish émigré, came to the United States in 1939 to work at Armco Steel in Middletown, Ohio. Sendzimir had earlier developed radical processes for galvanizing steel (1931) and cold rolling steel (1933). Sendzimir's rolling process departed dramatically from the multi-stand continuous process developed by John Tytus Armco (1924). Instead of using multi-stand four high rolls Sendzimir's mill used a clustered nest of rolls, like two inverted pyramids (1-2-3-4 configuration). A few Sendzimir Mills were built in Europe before WW II stopped construction of experimental steel plants. While Sendzimir was working at Armco, Signode Steel in Chicago ordered on of his "Z" Mills (Sendzimir Mills are called "Z" Mills in the United States). Signode used the mill to successfully roll low carbon steel for strapping and more importantly for rolling ultra thin silicon steel (for radar units) during WW II.
Stainless steel, first developed around 1915, is made by alloying carbon steel with chromium to make a metal that is highly resistant to corrosion. Stainless steel is relatively hard and is difficult to weld, cut, or drill. The physical properties of stainless steel are important to understanding why the "Z" mill has been so successful. Stainless steel was traditionally rolled in sheets on a four high reversing mill (with a Z mill much larger strips forming rolls can be made). Because stainless steel work hardens quickly it cannot be run through a multi-stand mill easily. One advantage of the a Z mill is that the small work rolls provide a sharper bite, greater pressure, and less roll deflection than a four high mill and thus can roll stainless top gage without having to anneal (soften) the roll.
For more on Sendzimir as an inventor see Steel Will: The Life of Tad Sendizmir, Hippocrene Books, New York, 1994 and by Vanda Sendzimir or "My Father the Inventor" in Invention and Technology, Fall 1995, p. 54-63 also by Vanda Sendzimir.