Zigzagging control method for workpiece

A zigzagging control method for a workpiece in a rolling mill of four-high or more,

• the rolling mill including a plurality of rolls that include at least a pair of work rolls including an upper work roll and a lower work roll and at least a pair of backup rolls including an upper backup roll and a lower backup roll supporting the work rolls,
• an upper roll assembly including the upper work roll and the upper backup roll,
• a lower roll assembly including the lower work roll and the lower backup roll,
• the zigzagging control method comprising:
• an estimation step of acquiring at least any one of an inter-roll thrust force estimated based on an inter-roll cross angle and an inter-roll friction coefficient that are acquired through measurement or estimation and a material-roll thrust force estimated based on a material-roll cross angle and a material-roll friction coefficient that are acquired through measurement or estimation, the estimation step being performed before rolling of a tail portion of the workpiece;
• and
• a tail control step of measuring work-side and drive-side rolling loads of at least any one of the upper and lower roll assemblies, correcting rolling-load-difference information based on any two of acquired parameters including a roll-axis-direction thrust counterforce at the measurement of the rolling loads, the inter-roll thrust force, and the material-roll thrust force that act on a roll other than the backup roll, the rolling-load-difference information being calculated based on the measured work-side and drive-side rolling loads, and performing reduction leveling control on the rolling mill based on the corrected rolling-load-difference information, the tail control step being performed during the rolling of the tail portion of the workpiece.