Dynamic Characteristics of Roll Push-Up Cylinder Based on Direct-Operated Servo Valve.

Force-motor direct-operated servo valves are increasingly used to improve the thickness control accuracy of hydraulic screw-down systems in rolling mills. The authors have proposed to use expandable, compressible metal springs instead of conventional rubber springs to position the spool in a servo valve, and a unique method to damp it with eddy current. The experiment on commercially operated mills has proven that the metal-spring valve exhibits excellent system response compared to the rubber-spring valve, though the independent response of the former is lower than the latter. Furthermore, a simulation study of dynamic characteristics of servo valves to control the roll push-up cylinder under an intended load was conducted using mathematical models in quadratic form considering complex or viscous damping. The result generally agreed with that of experiment and clarified that damping characteristics of the valve and the spring constant of the spool-supporting spring have significant influence on frequency response of the roll push-up cylinder.