PURPOSE: To prevent over reduction without imparting restraining force of metal strip by switching hydraulic reduction control mode from isobaric reduction load control mode to isobaric reduction position control mode in the case a difference between operating side and driving side is turned to larger than a prescribed set value.
CONSTITUTION: The difference in operating side/driving side reduction position signals, which are measured by operating side and driving side reduction position detectors 13, 14, is operating by a measuring-comparision arithmetic unit 20 and is compared to the reducing position set value set beforehand. When a difference in reduction positions is larger than a prescribed value, a hydraulic reduction controller 30 controls hydraulic reduction in response to reduction position target with switching hydraulic reduction control mode from isobaric reduction load control mode to isobaric reduction position control mode. The difference in operating side/driving side rolling load signals, which is measured by operating side/driving side rolling load detectors 15, 16, is operated and is compared to reduction load set value, when a difference in reduction loads is smaller than the prescribed set value, the controller 30 executes hydraulic reduction control with switching hydraulic reduction control mode from isobaric reduction load mode to isobaric reduction position control mode.
KURODA SHIGERU
HIROYAMA KAZUTOSHI
