Chapter 17: Rolling of Metals

The text differentiates between hot rolling, used for the initial breakdown of ingots into semifinished products like blooms, billets, and slabs, and cold rolling, which produces sheet, strip, and foil with superior surface finish and dimensional tolerances. A significant portion of the chapter is dedicated to the mechanics of rolling, detailing the forces involved, the concept of the friction hill, and the neutral point (no-slip point) where the velocity of the strip matches the roll speed. It explores the geometrical relationships in the roll gap, including the angle of bite and the limiting conditions for unaided entry based on the coefficient of friction. Theoretical frameworks for analyzing rolling loads are examined, ranging from simplified plane-strain analyses to complex theories for cold rolling proposed by von Karman, Orowan, and Bland and Ford, as well as hot rolling theories that account for strain rate sensitivity and sticking friction. The chapter also discusses critical equipment configurations, such as two-high, three-high, and four-high mills, alongside specialized setups like the planetary mill and cluster mills (Sendzimir) designed to minimize roll deflection. Furthermore, it addresses practical operational challenges, including roll flattening (analyzed via Hitchcock's formula), mill spring, and the elastic distortion of the mill housing. The summary covers defects inherent to the process, such as edge cracking, alligatoring caused by secondary tensile stresses, and shape problems like wavy edges or center buckles resulting from inhomogeneous deformation. Finally, the text explains modern rolling-mill control, utilizing elastic and plastic characteristic curves to manage gauge control and compensate for variables like back tension and friction to ensure product uniformity.