Aluminium hot mill work roll cooling control

In an ongoing program to improve both strip shape and profile control on an aluminium hot mill, a new work-roll cooling spray system with the capability of independent temperature control of narrow zones across the width of the rolls was purchased and installed. Time-proportioned on/off valve control was selected to provide coolant flow variation. Inherent problems with on/off control of individual valves are discussed. They include thermal lobes, hydraulic hammers, and thermal waves. Each of these problems was addressed and the solution integrated in the control system design.<>